This took me a long, long time. Also i didn't include all the games made by a dev, just the main ones :

Rockstar Leeds (GTA : VC Stories, GTA : LC Stories, GTA : Chinatown Wars)
Rockstar London (Most of Manhunt 2)
Rockstar North / Prev. DMA Design (Lemmings, GTA main series, Manhunt 1)
Rockstar Lincoln (Grand Theft Auto : Game Boy Colour)
Codemasters (Brian Lara Cricket series, Clin McRea Rally series, Race Driver : GRID,  Formula One 2009, Psycho Pinball, Operation Flashpoint 2)
DR Studios (Hospital Tycoon, Monopoly Tycoon, Risk 2, Tycoon City : NY, Beach Life, Sea World Tycoon series)
Frontier Developments (Rollercoaster Tycoon series, Wallace & gromit series, Thrillville series, Lost winds WiiWare, The Outsider)
Ninja Theory (Heavenly Sword, Kung Fu Chaos)
Criterion Software (Burnout series, Black, Airblade, TrickStyle, Suzuki Alstare Racing, Redline Racer, Sub Culture, Scorched Planet) 
Evoloution studios (Motorstorm series, World Rally Championship series)
Travellers Tales (Toy Story series, Sonic 3D Blast, Crash Bandicoot : Wrath of Cortex, Transformers : The Game, Lego Star Wars series, Lego Batman, Chronicles Of Narnia series, Bionicle Heroes, Super Monkey Ball Adventures, Finding Nemo, The Weakest Link, A Bug's Life, F1 Grand Prix, WRC : FIA World Rally Championship)
Bizzare Creations (Project Gotham Racing series, Treasure Planet, Geometry Wars XBLA series, The Club, Metropolis Street Racer)
Lionhead Studios (Black & White series, The Movies, Fable series) 
Rare LTD. (Banjo Kazooie series, Battletoads series, Conker series, Long list of Donkey Kong and Diddy Kong titles and spin-ofs, Goldeneye 007, Hollywood Squares, It's Mr Pants, Jetpac Refuelled, Jetforce Gemini, Killer Instinct, Perfect Dark 64, Perfect Dark Zero, Sesame Street 1-2-3 and ABC, Star Fox Adventures, Viva Piniata series, Who framed Roger Rabbit ?, WWF WrestleMania)
Media Molecule (Little Big Planet)
Eurocom (James Bond 007 : Nightfire, Athens 2004, Beijing 2008, Batman Begins, Pirates Of The Carribean : At Worlds End, Ice Age 2, The Mummy : Tomb of the Dragon Raider)
BigBig studios (Pursuit Force series)
SCE London studio (The Getaway series, Eyetoy series, Singstar series, This is Football series, World Tour Soccor series, Beats, Fired Up, Playstation Home, Eight Days (Cancelled))
SCE Studio Cambridge (MediEvil series, Ghost Hunter, Primal, 24 : The Game)
SCE Studio Liverpool (F1 series 2001 to 2006, Wipeout series, Krazy Ivan, Colony Wars : Vengeance, All the lemming spin-offs after original)
Realtime worlds (APB, Crackdown)
Sports Interactive (Championship Manager series, Football Manager series, NHL Eastside Hockey Manager serie,  Championship Manager Quiz)
Free Radical Design (Timesplitters series, Second Sight, Haze, Lucas Arts Unnanounced Project Rumored to be Battlefront 3)
Sega Racing Studio (Sega Rally Revo, Sega Rally 3 2009)
Zoe Mode (A few Eyetoy and Singstar's in collaboration with SCE London, Crush, Rock Revoloution, You're In The Movies, Dancing With The Stars, Disney Sing It)
Chemistry (Sensible Soccer 2006,  LMA Proffesional Manager 2005, some ports)
Juice games (Juiced series)
Rebellion Developments (Eye of the Storm, Alien Vs. Predator, Mission Impossible, PS1 ports of the first 2 Rainbow Six games, Lots of Game Boy and PSP ports, Rogue Trooper, Alien Vs Predator 2 Requiem, Ps2 PSP Wii versions of The Simpsons game, SW Battlefront : Renega Squadron)
Beautiful Game Studios (Championship Manager Games from 2005 to 09 atleast)
Magenta Software (Stuart Little 2 to 3,  3 Buzz spin-offs,  A Cat in the Hat, Muppet Adventures, Treasure Planet)
Gusto Games (Some Championship Manager ports, ProStroke Gold World Tour 2007)
Exient Entertainment (Lots and lots of EA franchise ports to protables and PS2 including NASCAR, Fifa, Madden NCAA Football, Need For Speed, Fifa World Cup, Fifa Street and once a WWE port)
Ubisoft Reflections (Shadow of the Beast series, Destrustion derby series,  Driver series, Emergency Heroes, Ballistix)
Team 17 (All the Worms games, Leisure Suit Larry : Box Office Bust, Some Lemmings ports)
Relentless Software (Main Buzz game and some spihn-offs, secret project)
Climax Group (Silent Hill:Origins, Ghost Rider, Viva Piniata PC Port, ATV series, MotoGP games upto 06, Hot Wheels games, Diablo PS1 port)
Sumo Digital (OutRun 2, OutRun 2006 : Coast 2 Coast, Go! Sodoku, Virtua Tennis 3, New International Track & Field, Untitled Racing Projet)
Splash Damage (Wolfenstein : Enemy Territory, Quake Wars : Enemy Territory, Unnanounced project with Bethesda Ltd.)
Creative assembely (Total Wars series, Viking Battle For Asgard, Spartan : Total Warrior)
Blitz Game Studios (Fuzion Frenzy 1, Barbie Horse Adventures : Wild Horse Rescue, Taz : Wanted, Sneak King, 2 Bratz games, 2 Karaoke Revoloution games, 2 SpongeBob Square Pants games)
EA UK closed in 2006 (All Harry Potter games before 06, some more licenses)
Atomic Planet Entertainment (Bob The Builder, Jenga, Arctic Tale, Sea Monsters : A Prehistoric Adventure, Charlotte's Web,  Jackie Chan Adventures, Mike Tyson Heavyweight Boxing, Robin Hood : Defender of the Crown)
Bitmap Brothers (Speedball series, The Chaos Engine series, Xenon series)
Eidos Interactive (Games listed are published only, not developed) (Age of Conan : Hyborian Adventures, Hitman series, Tomb Raider series, Kane & Lynch  (Go Gerstmann :-D), Deus Ex series, Just Cause series, Legacy of Kain series, Soul Bubbles Wii Ware, Thief series, Battlestations series, Doctor Who license)
Pivotal Games (Conflict series, The Great escape)
Firefly Studios (Stronghold series, CivCity : Rome, Space Colony, Dungeon Hero 2009)
Halch Development Studio (Bob The Builder : Festival of Fun, Secret projects)
Jagex Ltd. (Runescape, Runescape HD)   
Linux Game Publishing (I'm getting lazy now and need a brake so basically their just developing some casual crap that no-one cares about, Ok)
Jeff Minter/Llamasoft (Space Giraffe XBLA, some old retro games along time ago) 
Monumental Games (Football Superstars MMO)
Mucky Foot Productions closed 2003 (Urban Chaos, Startopia, Blade 2)
Oxygen Studios (Pirates : The Key Of Dreams WiiWare, Pirates Dual on the High Seas, Chegger's Party Quiz, King Of Clubs)
Oxygen Games (Totally seperate from above) (Alan Hansens Sports Challenge, 8Ball Allstars, PDC World Championship Darts)
PixelCubed Games (Kingdom Of Old)
Rocksteady Studios (Urban chaos)

nice :D

Very nice.  Comprehensive list.

omg runecape was made in the UK D:

It's wierd but some games are listed twice for different devs :s
I blame it on Wikipidia :p

I do know Singstar is made in London perhaps